The integration of Monolithic Millimeter Wave Integrated Circuits (MMICs) into high frequency communication systems and devices has increased the need for a low cost packaging system that can be mass produced. These systems are currently operating at 50 GHz and above, but currently available, conventional packaging techniques are typically inadequate for such high frequency devices because they fail to adequately transmit the signal without any resonance from DC to mm-wave and thus result in a loss with every transition. Most V-band and W-band MMIC packages available today have narrow operating bandwidths and offer only single-ended inputs and outputs (I/Os).
Traditionally, integrated circuits (IC) formed on a semiconductor chip are packaged by enclosing the chip within a plastic or ceramic casing, attaching wire bonds between the pads of the chip and the package leads, and then soldering the leads to a circuit board. Ceramic packaging such as co-fired ceramic enclosures are commonly used for housing small ICs and other solid-state electronic devices. The IC is typically housed in or on a ceramic substrate, or in a cavity within the substrate, and metallized feed-throughs connect the integrated circuit with the outside of the package. The package may have a metal base or core that serves as a ground plane, and may further incorporate a metal slug for improved heat removal.
Commonly, thick film or screen printing techniques are used to form conductive traces on the substrate, and metal leads such as Kovar™ or copper ribbons are then soldered or brazed onto the metal traces to provide connections from the package to exterior circuitry. This technique is acceptable for low frequency devices but when applied to high frequency devices however, the millimeter components corresponding to the high frequency components of the signal exhibit odd behavior because the standard package cannot carry the high frequency signal. These losses and the erratic signal behavior occur as a result of the internal structure of the package and the signal transitioning from one package down to the circuit board and back up into another package. In particular, printed feed-throughs have to be matched to a transmission line, which is typically a microstrip that is printed on the circuit board, and wire bonds, ribbon bonds, or leads at this point create an inductance that can result in undesirable insertion losses at higher frequencies.
For high frequency (i.e. microwave and millimeter wave frequencies) IC packaging, controlled impedance feed-throughs and interconnections are typically provided to control signal reflections and losses to acceptable levels. This entails careful design of conductor geometry, which requires consideration of dielectric thickness and permittivity, as well as ground geometry. At high frequencies, many feed-through structures will support higher order modes of transmission and resonances, and have dispersive propagation degrading characteristics (i.e., frequency-dependent characteristic impedance and propagation velocity) thereby degrading signal fidelity. To reduce or minimize these deleterious effects, thinner dielectric substrates are preferable.
Because the traces on a well-designed microwave package are themselves controlled impedance transmission lines and the interconnect substrate can typically be a printed circuit board of appropriate material and thickness for high frequency operation, it is desirable to maintain the lead lengths between the package and the printed circuit board traces as short as possible to achieve broadband performance (typically, DC to 40 GHz or more) with low-loss interconnection. Surface-mounting the ICs, wherein all package signal and ground connections lie in the same plane, are known to address these issues. Typical surface-mount packages employ metallic vias through the dielectric (e.g. ceramic) layer to transfer both signal and ground connections from the device to the package mounting surface (typically a metal chassis), as well as carry much of the heat generated by the packaged device to the chassis.
In view of the above, there is an ongoing quest for a packaging solution that will allow the nonplanar transmission line connectors on the package to be connected to the planar line conductors on the printed circuit board with a minimum of signal loss. The packaging will preferably also simplify the installation as well as replacement of the packaged ICs within the overall system, facilitate multi-chip assembly, and be applicable to multi-port ICs. Conventional methods for assembling a module having multiple chips entail numerous, time-consuming, and mistake-riddled prototype iterations before a final design is produced. Accordingly, what is now needed is a method and design for packaging high speed ICs that offers ease of assembly and re-assembly, is low-cost to produce and use, and provides acceptable performance at high IC operating frequencies. The embodiments disclosed herein answer these and other needs.